(1) Field of the Invention
This invention relates to a bar light source for an edge light panel that supplies incident light into an edge light panel for area illumination. The present invention also relates to an illumination sign device using the bar light source.
(2) Description of the Related Art
The edge light panel (refereed to as a light guiding plate) of that type for area illumination is used as a liquid crystal back lighting function mounted on, for example, a liquid crystal display device, or as an illumination signboard display stand.
The edge light panel is generally formed of a transparent substrate of transparent acrylic resin and has one end surface or plural end surfaces acting as incident end surfaces. The edge light panel is formed by printing a light guiding pattern formed of meshed dots for incident light guidance on the back surface thereof and then processing the intermediate product. The edge light panel may be formed by one-piece molding upon forming a transparent substrate. To order to supply incident light to the incident end surface of an edge light panel, a hot cathode or cold cathode fluorescent light source is mounted adjacent to the incident end surface. The light guiding pattern guides incident light to provide area illumination.
In such a configuration, the edge light panel can preferably convert the incident light from the fluorescent light source into area illumination with high brightness and high uniformity. However, there is the disadvantage in that the fluorescent light source used for the edge light panel radiates heat and must be replaced every time its serviceable life ends. The cold cathode fluorescent light source improves the disadvantage of the cold fluorescent light source, but cannot solve the basic problems described above.
The heat radiated from the fluorescent light source rises the temperature of the edge light panel, the liquid crystal display surface under the liquid crystal back light, the film or panel for an illumination signboard to be illuminated, or the like, thus affecting adversely them. The exchange work of a terminated lamp requires disassembling the liquid crystal device, illumination signboard, or the like. A road sign using an edge light panel, for example, installed at an elevated place requires an exchanging work at a high place. These disadvantages result in complicated works.